1. Field
The present disclosure relates generally to communications systems, and more specifically, to systems and techniques for the reacquisition of a gated pilot signal.
2. Background
Modern communications systems are designed to allow multiple users to share a common communications medium. One such communications system is a code division multiple access (CDMA) system. The CDMA communications system is a modulation and multiple access scheme based on spread-spectrum communications. In a CDMA communications system, a large number of signals share the same frequency spectrum and, as a result, provide an increase in user capacity. This is achieved by transmitting each signal with a different pseudo-noise (PN) code that modulates a carrier, and thereby, spreads the spectrum of the signal waveform. The transmitted signals are separated in the receiver by a correlator that uses a corresponding PN code to despread the desired signal's spectrum. The undesired signals, whose PN codes do not match, are not despread in bandwidth and contribute only to noise.
In a CDMA communications system, a subscriber station may access a network, or communicate with other subscriber stations, through one or more base stations. Each base station is configured to serve all subscriber stations in a specific geographic region generally referred to as a cell. In some high traffic applications, the cell may be divided into sectors with a base station serving each sector. Each base station transmits a continuous pilot signal which is used by the subscriber stations for synchronizing with a base station and to provide coherent demodulation of the transmitted signal once the subscriber station is synchronized to the base station. The subscriber station generally establishes a communications channel with the base station having the strongest pilot signal.
Since a continuous pilot signal requires bandwidth that could otherwise be used to transmit information, some recently developed CDMA communications systems, such as IS-856, have employed gated pilot signals. A gated pilot signal is characterized by a short period of transmission of pilot signal followed by a long period of no transmission. By gating the pilot signal, additional bandwidth can be realized which increases the capacity of the base station. However, acquisition of gated pilot signal takes a longer time than acquisition of a continuous pilot signal. If the mobile performs frequent re-acquisitions, long delays wasted for re-acquisition can deteriorate the quality of data service offered by the subscriber stations. Thus, what is needed is a system and method to reduce the time it takes to re-acquire a gated pilot signal after it has been lost.
It would be apparent to those skilled in the art that any communications system and method that uses a gated pilot signal can benefit from a system and method to reduce the time it takes to re-acquire the gated pilot signal.
Systems and techniques for acquisition of a gated pilot are described in U.S. patent application No., “Acquisition of a Gated Pilot,” Ser. No. 09/927,869, filed Aug. 9, 2001. Systems and techniques for acquisition of a gated pilot are disclosed wherein a gated pilot signal can be acquired by searching for a first gated pilot signal, deriving timing information from the search for the first gated pilot signal, and searching for a second gated pilot signal using the timing information.
Systems and techniques for acquisition of a gated pilot by avoiding partial correlation peaks are described in U.S. patent application No., “Acquisition of a Gated Pilot By Avoiding Partial Correlation Peaks,” Ser. No. 09/895,657, filed Jun. 29, 2001. Systems and techniques are disclosed wherein a gated pilot signal can be acquired faster by checking the neighbor pilot signals of the target pilot signal.